1. Field of the Invention
The present invention relates to FM-CW range and relative speed measuring devices.
2. Description of the Prior Art
A device of the kind to which the invention relates is described in German Pat. No. 867,709. The device described therein is a frequency-modulated continuous-wave radar device, which will hereinafter be referred to as an "FM-CW device." In such FM-CW equipment, superposition of the signals reflected from the target on the local signal results in distance-and-speed dependent beat-note signals from which distance and relative speed may be determined.
The particular embodiments described in the aforementioned representative prior art can be divided into two groups, viz; those which determine speed and range simultaneously, and those which make those measurements sequentially.
In the first instance, two transmitter-receiver units are required. To measure distance, (range), a signal frequency-modulated in a sawtooth mode is radiated by the first transmitter. To measure the relative speed, an unmodulated signal is simultaneously radiated by the second transmitter. The evaluation of distance and relative speed reflection signals takes place simultaneously in the receivers.
In the second instance, only one transmitter-receiver unit is required, which alternately transmits frequency-modulated and unmodulated signals; or alternatively, the transmissions may be frequency-modulated in a triangular mode. The received signals are evaluated with respect to distance and relative speed one after the other or, if suitable storages are provided, they may be contemporaneously processed albeit not entirely in real time. If the radiated signals are exclusively those frequency-modulated in a triangular mode, the sign of the relative speed cannot be determined.